From: "matz (Yukihiro Matsumoto) via ruby-core" <ruby-core@...>
Date: 2026-09-10T09:53:25+00:00
Subject: [ruby-core:126643] [Ruby Bug#22273] Aliasing doesn't interact well with Module#prepend

Issue #22273 has been updated by matz (Yukihiro Matsumoto).


I accept Jeremy's proposal. `alias` should look up the method from the origin class, so it only sees the methods of the class/module itself and its ancestors. Aliasing a method that exists only in a prepended module should raise `NameError`.

This reverses my decision in #7842. `alias` is an operation on definitions like `def` and `remove_method`, not a method lookup from outside. Prepended modules are layers in front of those definitions, so `alias` should not capture them. This is also the same principle as #22276.

If you want an alias that goes through prepended modules, define a forwarding method (e.g. `def a(...) = b(...)`) instead.

I leave the migration path to the implementer.

Matz.

----------------------------------------
Bug #22273: Aliasing doesn't interact well with Module#prepend
https://bugs.ruby-lang.org/issues/22273#change-118898

* Author: luke-gru (Luke Gruber)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
Currently, aliasing doesn't interact well with `Module#prepend` in my opinion.

### Example

```ruby
module Kernel
  prepend(Module.new do
    def require(feature)
      puts "requiring feature (prepend): #{feature}"
      super
    end
  end)
end

module Kernel
  alias original_require require
  def require(feature)
    puts "requiring feature (alias): #{feature}"
    original_require(feature)
  end
end

require "set"
```

This produces this behavior:

```
requiring feature (prepend): set
requiring feature (alias): set
requiring feature (prepend): set
../ruby/test.rb:5:in 'require': super: no superclass method 'require' for main (NoMethodError)
```

I would expect this behavior:

```
requiring feature (prepend): set
requiring feature (alias): set
# Then, the original require would succeed
```

This has caused issues such as [22263](https://bugs.ruby-lang.org/issues/22263) and has [confused gem authors](https://github.com/fxn/zeitwerk/pull/203#issuecomment-1107777206). In the second link, the ignored alias was due to [this bug](https://github.com/ruby/ruby/commit/c59c4d717a2e687972341eab1574196e97d7d7be) which has recently been fixed.

### Bug?

As far as I know this is intentional behavior introduced in Ruby 2.0 [here](https://bugs.ruby-lang.org/issues/7842). There are even tests and specs that codify this behavior such as `test_prepend_super_in_alias` and `prepend_spec.rb`.

Even though it's intentional, I don't believe it's well thought out. I'm interested in hearing arguments for and against the current behavior (with code examples, preferably).



-- 
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